Acid resisting vitreous enamel



Patented Feb. 12, 1935 A011) 'RE-SISTING VITREOUS ENAMEL Perry G. Bartlett and Harry G. Kremers, Philadelphia, Pa., assignors to Riihm & Haas Company, Philadelphia, Pa.

' No Drawing.

. This application relates to vitreous enamels. It has for its object the preparation of a dry process enamel which is acid resistant and capable of use in conjunction with zirconium com- 5 pounds as opacifier. A further object is theuse of glass cullet in the preparation of acid resisting vitreous enamels. Other objects will be developed below.

Ordinary'dry process enamels for cast iron are readily attacked by common fruit, and vegetable juices and also by the harsher cleansing materials. These substances remove the gloss from the enamel surface and leave a rough spot which soon becomes permanently stained and discolored.

Dry process enamels have beendeveloped possessing various degrees of resistance to those acids present in the fruit and vegetable juices, which ordinarily stain the ware.

The variation in dewhich comparisons can be made.

We 5' have adopted for this purpose the test which is most commonly used in the trade, and is the nearest of any to becoming the standard test for acid resistance. Only those enamels which are not visibly stained after a drop of fresh 10% citric acid solution has remained on them for 15 minutes, are considered to be acid resistant. Hereafter, in this application the term'acid-resistance is used only in that sense. Enamels which are resistant according to this test also resist quite successfully the action of the 'stronginorganic, or mineral acids such'as sulphuric, hydrochloric and nitric acids. Alkali resistance may similarly be defined ascomplete resistance to'strong caustic (NaOI-I) solution. when evaporated to dryness on the enamel surface. Alkali resistance isused inthis application with that significance.

. Acid resisting dry process enamels,

las for tin and antimony acid are given below:

resisting enamels Tin. oxide, acid resistant enamel (1) Percentage composition of melted batch (2) Raw batch mixture 7 (3) Seger or molecular formula trate 42 Fluorspar 22 Red lead- 122- Feldspar 177 Sodium silicater --282 Sodium. titanium silicate 163$ Tin oxide.-- 92 Borax --100 Application February 5, 1932, Serial No. 591,241

'8 Claims. (CL 106-362) Sodium antimonate, acid resistant enamel (1) Percentage composition of (2) Raw batch mixture (3) Sager or molecular formula melted batch Nam... 17.0% Soda ash 13 NazO. .686 SiO2 1. 712 K90.... 5.0 Potassium K20 .133 A TiO2 .219 ZnO 2.0 nitrate..- 01 2110-- .063 3 $1020.. 078 CaO 1.0 Zincoxide.. 18 0210.. .045 B203" 236 PbO 6.5 Whiting--- 16 PbO .073 F2.-- .060 B203.-- 6.6 Red lead--- 58 a .9 Borax 157 1.000 2 305 A1203-.- 3.0 Cryolita-.. 15 Y '07-- .0 Fe1dspar 124 TiOi 7.0 Sod.silicate 372 Sb2O5- 10.0 Titanium oxide..-" 61 100. 0% Sodium antimonate- 105 Zirconium compounds as opacifiers have distinct advantages over other opacifying materials. They are cheaper to obtain than tin oxide and give a better color. As compared with compounds of antimonyzirconium compounds are to be preferred because of their non-poisonous character, their inertness and irreducib ility. Their inert character renders them-less susceptible to varia-'.- tion in manufacturing rocesses- No acid resistant enamels opacified with zirconium compounds have been previously developed. Now we have discovered an enamel which combines the advantages of acid-resistance and alkali-resistance together with the advantagesof using" zirconium compounds to give opacity. In order to develop such an enamel it was'necessary enamel formula; This new type of formulaiis characterized by its high zinc oxide, silica and titanium dioxide content, and by the complete absence of boric oxide and fluorine compounds. Several'typical examplesof this type of formula are as follows:

Example (1) lercentage composition of melted batch (2) Raw batch mixture N320.-- 13.5 K2 4.5 Mg -1- 0.9 ZnO-- l0. 0 08.0-.-- 1. Pb 7.8 A1203- 3.3

'02.--- 37.7 TiOz'..- O Zl'Oz.-- 10.8

Soda ash 94 Potassium nitrate"; 53 Zinc oxide. 92 'Red lead- 74 Feldspar 106 Glasscullet 389 Titanium dioxide.-- Zirconium oxide..-" 100 are; as as: as at 0.10.- .057 TOLL PbO 074 L780 Example 2 (1) Percentage (2) R b t h composition of a c (3) Seger or molecular formula melted batch N8IO 13.0 Potassium NazO- ..446 1110...- 4.0 ni ate.-- 2 K10.-. 1 Sio 1 345 MgO 1.0 Zincoxide" 106 Mg .053. AlrOa 1' ZnO. 11.0 Magnesia 10 Zn0 1.083 ,195 0110-. 1.0 Whiting.-- 17 Goo.-- PbO 8.8 Litharge 85 H10... .084 1 7797 A1101..- 3.0 Feldspar... 159 $102..-- 38.0 Sodium sili- TiOz--- 9.0 to 284 ZrOz.-- 11.2 Titanium dioxide 87 100. 0% Sodium zirconium silicateni. 192 Zirconium silicate 18 Example 3 NazO-.- 14.4 ,Sodaasln- 72 Na:0- ..52l 1:10-.-- 2.6 Sod. m 20... .003 A120: 33? ggg zno 1115 trate as Zno .319 .087 se 2-s $82 W a r. a par. 8101;... 40.0 Sod. .sili- 1.000 L888 T101.-. 6.0 cats"-.- 287: I Zl'Oz-.- 12.0 Titanium 1 dioxide..- 56 100.0% Red lead 92 Zirconium g oxide 56 Zirconium silicate 85,

Example 4 I NaaO... 13:0 Soda ash; 8;5 Nam" .444 K 01.-- 4.5 yPOt; ni' K10- 101 sin 310 M20--- 0.9 trete -3 MEOa. .0 6 A1203 0 2110;... 10.5 Zineoxido. 9.7 Zn0' .2741068 Cool.-. 1.5 lead 7. 9,- CaO- .0573 PbO 8L2 Feldspar l0.8 PbO.. .078 1 761 Altos." 3:3 38 5: SiOh.-. 37.3 Titanium 1.000 TiOr..- 10.0 dioxide" 9 3 ZrOz--- 10.8 Zirconium oxide-.. 10.0 1(X).0%

A frit composition of the. abovematerials ismade upin the usual well known manner, i. e. by fusing them at a hightemperature in a smelting furnace, quenching in water, drying and grinding. The'dry enamelingv process. is carried out one cast iron article and the enamel passes very successfully the aforementioned tests for acid and alkali resistance.

These formulas are characteristic of the type gives an enamel having the desired properties. Howevenit should be clearly understood that we are not limited to these four, or any other formula. All of the above components may be varied within certain limits and still give a. commercially practical. enamel. V

The limits of variation of the different components have been determined experimentally to be as follows; it being understood that slight variations can possibly be made.

1. The percentage of alkalies (NazO) and (X20) present m the finishedenamel may vary from 15.0 to 19.51%, depending on thezinc and lead content. Of this alkali percentage, :not less than .2 or more than 7% may be potash. (K20).

2. Magnesia and lime (CaO) not essential constituents of these enamelsfand may be replaced entirely by zinc oxide. The maximum amount of either 09.0 or MgO which may be present is 2%.

3. Zinc oxide must constitute at least 8% of the weight of the. melted batch. The-maximum amount depends onthe alkali and leadoxide con- 7 tent, but cannot exceed 12%.

4. The percentage of lead oxide used depends on the alkalies and the zinc oxide present, but in any case is limited to between 5.5 and 12.0%.

5. The refractory oxides present in the melted batch, which are alumina, silica, titanium oxide and zirconium oxide. must total 60-65% in order to give acid resistance. Each one of these refractory oxides may vary somewhat, depending upon the amounts of the others present. The limitsv for each one have been determined to be as follows: alumina (A1203): 2 4.5%, silica (S102) 36.5-43-%, titanium dioxide (TlOs): 540.5%, and zirconium oxide (ZrOz): 95-12%.

The limits of variation of the enamel-cornponents have been defined in terms of percentage weightin the melted batch, or in other words, by the analysis, because it is the final compositionrather than the raw materials used which determine the properties of the enamel itself. 'Wlth only two exceptions, the properties of an enamel depend on final composition rather than them.- ture of the raw materials used to obtain this. final composition. Some nitrates, usually so dium or potassium nitrates, are essential'in the raw batch mixture in order to maintain an aid-- dizing atmosphere in the furnace during smelting. Otherwise, reduction of certainmetalox ides, particularly titanium dioxide, will occur and the resulting enamel will be discolored. Also, it

is necessary to addsilica to the raw batch ina combined form such as feldspar, sodium silicate, or ground glass cullet'. Free silica, added as flint; ground quartz or sand, necessitates prolonged smelting in order toobtain complete fusion, and the prolonged smelting is detrimental to the enamel opacity.

However, with these two exceptions, it makes comparatively littl'edifl'erence whether lead is added as red lead, or as litharge; soda added as: soda ash, sodium silicate or sodium nitrate: alumina added as glass cullet, feldspar or alumi-- num; hydrate, and so forth. I

Scrapped glass or cullet has not previously been used: as an acid-resistant: enamel raw ma terial. We find that; it is an excellent material for furnishing silica and soda. as well as small amounts of alumina, potash, lime and magnsia.

It can be added in such an amount: as: tobring the total SiOz content of the melted between 36.5% to 43%, the proportions ofthe other ingredients being kept within the limits specified. I I

Any ofi the zirconium compounds ordinarily used as opacifiers can be used in these compost; tions. The most desirable compoundsare zirconium silicate, zirconium oxide, alkali and alkaline earth zirconium silicates, zirconiumthydroxide, alkali and alkaline. earth, zirconates, and to a lesser degree, basic zirconium hydroxidegfand zirconium borates.

It isto beunderstood thatthe following claims include; only those variations-in percentage of in; gredients within the limits of commercially sat-i isfactory enamels, i. e. those which, will. give th e proper gloss, will have the proper coefll'cient] of expansion and the proper fusing behavior; Slight variations from the limits-set wiil fall scope of the invention.

We claim: 1 I

1. The step in dry process enameling which comprises coating heated articles with a fritcomposition containing in the melted batch zinc oxide 812%, alkalies 15-19.5% of which K may vary 2-'7%, lead oxide 55-12%, alumina 24.5%, silica 365-4370, titanium dioxide 5-10.5% and zirconium oxide 9.5-12%.

2. An enamel composition comprising in the melted batch the following:

Per cent Alkalies 15 -19.5 Magnesia and lime 0 2 Zinc oxide 8 -12 Lead oxide 5.5-12 Alumina 2 4.5 Silica 36.5 43 Titanium dioxide 5 10.5 Zirconium oxide 9.5-12

3. An enamel composition comprising in the melted batch the following in substantially the percentages given:

4. An enamel composition comprising in the melted batch the following in substantially the percentages given:

Na20 14.4 K20 2.6 ZnO 11.5 PbO 9.5 A1203 4.0 S102 40.0 TiOz 6.0 ZrOz 12.0

5. An enamel composition comprising in the melted batch the following in substantially the percentages given:

6. In the process of preparing a dry process acid resisting enamel free of boric acid and fluorides the step of adding glass cullet, which is also free of boric acid and fluorides to the raw batch mixture to bring the total $102 content of the melted batch to between 36.5% to 43.0%.

'7. The step in dry process enameling which comprises coating heated articles with a frit composition free of boric oxide and fluorides, containing as basic constituents alkalies, alkaline earths, zinc oxide and lead oxide, as refractory oxides those of aluminum, titanium and silicon and as an opacifler zirconium oxide, the sum of the refractory oxides and opacifler being between and of the melted batch.

8. The step in dry process enameling which comprises coating heated articles with a frit composition free of boric oxide and fluorides, containing as basic constituents alkalies, zinc oxide and lead oxide, as refractory oxides those of aluminum, titanium and silicon and as an opacifier zirconium oxide, the sum of the refractory oxides and opacifier being between 60% and 65% of the melted batch.

PERRY G. BARTLE'I'I'. HARRY c. KREMERS. 

